This invention relates to a new family of crystalline metal oxide compositions. These compositions contain tantalum, an alkali metal, at least one M metal where M is tungsten or molybdenum, optionally a Mxe2x80x2 metal such as vanadium or niobium and optionally a Mxe2x80x3 metal such as titanium or tin. This invention also relates to hydrocarbon conversion processes such as dehydrogenation using the composition.
Olefins, e.g., propylene or isobutene are used to prepare a number of higher value products such as aldehydes, acids and nitrites. Since the price of the corresponding alkanes, i.e., propane or isobutane is lower than that of the olefins, it would be advantageous to be able to produce the higher value product directly from the alkanes.
Attempts have been made to synthesize novel materials to catalyze the selective oxidation of paraffins. One such catalyst is described in U.S. Pat. No. 5,750,760 where it is disclosed that a multinary composition having the empirical formula:
MoaVbSbcXxOn
where X is an element such as Nb, Ta, W etc. can catalyze the oxidation of an alkane with ammonia in the presence of oxygen. Other compositions which have been disclosed in the art include a Mo4VO14 phase by H. Werner et al. in Catalysis Letters, 44 (1997) 153-63. In J. Catalysis 52, 116-132 (1978), E. M. Thorsteinson et al., describe a mixed oxide catalyst containing molybdenum and vanadium along with another transition metal such as Ti, Nb, Ta, etc. The authors present activity data and physically characterize the compositions. MoVNb systems have also been described in Applied Catalysis, 70 129-148 (1991) and Topics in Catalysis 3, 355-364 (1996). U.S. Pat. No. 4,524,236 discloses a composition containing molybdenum, vanadium, niobium, antimony plus at least one metal such as lithium, barium, titanium etc. U.S. Pat. No. 4,339,355 discloses a composition comprising MoaVbNbcXd, where X is Co, Cr, Cu, Fe, In, Mn and/or Y. It is further disclosed that the compositions have spinel or perovskite structures. In U.S. Pat. No. 4,596,787 a catalyst comprising MoaVbNbcSbdXe is disclosed, where X includes Li, Sc, Na, Fr, Ta, etc. U.S. Pat. No. 4,250,346 discloses a catalyst with an empirical formula of MoaXbYc, where X is Cr, Mn, Nb, Ta, Ti, V and/or W and Y=Bi, Ce, Co, Cu, Fe, K, Mg, Ni, P, Pb, Sb, Si, Sn, Ti and/or U. U.S. Pat. No. 4,892,856 discloses a catalyst having the composition MoaVbAcBdCeDfOx where A is tungsten or niobium, B is Fe, Cu, Bi, Cr, Sb or TI, C is an alkali or alkaline earth metal and D is Si, Al or Ti. U.S. Pat. No. 5,807,531 discloses a multimetaloxide having an empirical formula of Mo12-a-b-cVaM1bM2cOx. However, these materials have a low surface area of 17 m2/g or lower. Finally, Ueda et al., in Chem. Commun., 1999, 517-518, disclose Moxe2x80x94Vxe2x80x94Mxe2x80x94O (M=Al, Fe, Cr and Ti) compositions which are hydrothermally synthesized, and in Applied Catalysis: General, 2000, 135-143, disclose Moxe2x80x94Vxe2x80x94Mxe2x80x94O (M=Al, Sb, Bi, Te) compositions which are hydrothermally synthesized. Although these compositions have a diffraction peak at about 3.9 xc3x85, they do not have applicant""s empirical formula (see below).
In contrast to these reports, applicants have synthesized a new family of crystalline oxide compositions based on tantalum, at least one of tungsten and molybdenum, and optionally another metal such as vanadium, niobium, antimony or tellurium. These novel compositions are prepared hydrothermally and are characterized in that they have an x-ray diffraction pattern with at least one peak at a d spacing of about 3.9 xc3x85 and a high surface area. These materials show good activity for dehydrogenation of hydrocarbons.
As stated, this invention relates to a new family of crystalline compositions and processes which use the compositions. Accordingly, one embodiment of the invention is a crystalline metal oxide composition having an empirical formula of:
AnTaMxMxe2x80x2yMxe2x80x3mOp
where A is an alkali metal ion, ammonium ion or mixtures thereof, M is selected from the group consisting of molybdenum, tungsten or mixtures thereof, Mxe2x80x2 is vanadium, antimony, tellurium, niobium and mixtures thereof and Mxe2x80x3 is selected from the group consisting of tin, titanium, indium, gallium, aluminum, bismuth and mixtures thereof, xe2x80x9cnxe2x80x9d varies from about 0.1 to about 2, xe2x80x9cxxe2x80x9d varies from about 0.01 to about 8, xe2x80x9cyxe2x80x9d varies from zero to about 4, xe2x80x9cmxe2x80x9d varies from zero to about 0.9 and xe2x80x9cpxe2x80x9d has a value such that it balances the valence of the combined elements A, Ta, M, Mxe2x80x2, Mxe2x80x3, the composition characterized in that it has at least one x-ray diffraction peak at a d spacing of about 3.9xc2x10.15 xc3x85.
Yet another embodiment of the invention is a hydrocarbon conversion process comprising contacting a hydrocarbon with a catalyst at hydrocarbon conversion conditions to give a hydroconverted product, the catalyst comprises one of the compositions described above.
These and other embodiments will become clearer after a detailed description of the invention.
A new family of crystalline metal oxide compositions has been synthesized and characterized. These compositions contain tantalum, at least one of tungsten and molybdenum, a third metal selected from vanadium niobium, antimony or tellurium and a fourth metal selected from tin, titanium, indium, gallium and mixtures thereof. A cation such as lithium is also present. These crystalline metal oxides are described by the empirical formula:
AnTaMxMxe2x80x2yMxe2x80x3mOp
where xe2x80x9cnxe2x80x9d varies from about 0.1 to about 2. The value of xe2x80x9cxxe2x80x9d varies from about 0.01 to about 8, while the value of xe2x80x9cyxe2x80x9d varies from zero to about 4 and the value of xe2x80x9cmxe2x80x9d varies from zero to about 0.9. M is molybdenum, tungsten, or mixtures thereof, Mxe2x80x2 is selected from the group consisting of vanadium, niobium, antimony, tellurium and mixtures thereof, while Mxe2x80x3 is tin, titanium, indium, gallium, aluminum, bismuth, and mixtures thereof. Finally, A is an alkali metal cation, an ammonium cation or mixtures thereof. Examples of the alkali metals which can be used include: lithium, sodium, potassium, rubidium, cesium and mixtures thereof.
These novel crystalline metal oxide compositions are hydrothermally prepared. That is, a reaction mixture is prepared from reactive sources of the desired components along with water and heated at a temperature and for a time sufficient to form the desired product. Reactive sources of the alkali metals include the hydroxide, carbonate, halide, acetate, and sulfate compounds. Niobium reactive sources include niobium pentoxide (Nb2O5), hydrous niobium oxide, niobium ethoxide, and ammonium niobium oxalate. Molybdenum sources include molybdic acid ((NH4)6Mo7O24.4H2O), molybdenum trioxide (MoO3), sodium molybdate and molybdenum (VI) oxychloride. Tungsten sources include ammonium tungstate, tungsten (VI) oxide, tungsten (VI) chloride, sodium tungstate, and tungstic acid. Vanadium sources include vanadium (V) oxide, vanadium (V) oxychloride, vanadium oxide sulfate, and ammonium vanadate. Tantalum sources include tantalum oxide, hydrous tantalum oxide, tantalum butoxide, tantalum bromide, and tantalum chloride. Tellurium sources include ammonium tellurium oxide, telluric acid, and tellurium oxide. Tin, indium, gallium, aluminum, and bismuth sources include the nitrates and chlorides, while titanium sources include titanium alkoxides, (NH4)2Ti(OH)2(C3H4O3)2 and TiCl3. It should be pointed out that this list is only by way of examples and other reactive sources of individual elements may also be used.
Using the above described reactive sources, a reaction mixture is formed which in terms of molar ratios of the oxides is expressed by the formula:
aA2O:TaO5/2:bMO3:cMxe2x80x2O5/2:dMxe2x80x3Oq/2:eH2O
where xe2x80x9caxe2x80x9d has a value from about 0.75 to about 4, xe2x80x9cbxe2x80x9d has a value of about 0.02 to about 10, xe2x80x9ccxe2x80x9d has a value from 0 to about 5, xe2x80x9cdxe2x80x9d has a value from 0 to about 1, xe2x80x9cqxe2x80x9d is the valence of Mxe2x80x3, xe2x80x9cexe2x80x9d has a value of about 10 to about 500. Once the reaction mixture is formed, it is required that it have a pH of about 4 to about 10 and preferably from about 6 to about 9. This can be done by using a basic compound of the A cation. Alternatively, the A cation can be added as a non-basic compound and the pH adjusted by the addition of an appropriate amount of an organic base such as an alkyl amine or a tetraalkylammonium hydroxide.
Once the reaction mixture is formed and pH adjusted, it is reacted at a temperature of about 100-225xc2x0 C. for a period of time of about 1 hr to about 350 hr in a sealed reaction vessel under autogenous pressure. After the allotted time, the mixture is filtered to isolate the solid product which is washed with deionized water and dried in air. Alternatively, the product may be isolated and washed by centrifugation techniques. The product may also be washed with aqueous acid rather than deionized water to convert the composition to the proton exchanged form during workup.
The crystalline metal oxide compositions of the invention are characterized by their unique x-ray diffraction pattern and their surface area. The x-ray diffraction pattern has at least one peak at a d spacing of about 3.9xc2x10.15 xc3x85. A second peak at xc2xd of the 3.9xc2x10.15 xc3x85 spacing is also often present in these compositions. Another X-ray diffraction peak, which is sometimes distinct but usually broad, is located at 10.7xc2x10.25 xc3x85. This peak is always broader than the 3.9 xc3x85 peak. Diffuse diffraction peaks are also located between 3.42 and 2.98 xc3x85.
The crystalline metal oxide compositions of the invention are also characterized by their surface areas. These materials generally have a surface area of at least 15 m2/g, and preferably at least 25 m2/g.
The above described compositions can be ion exchanged so that the A cation is exchanged for another, different, cation. These cations which can be exchanged into the metal oxide composition (secondary cations) include, without limitation, other alkali metal ions, hydronium ions, alkaline earth ions, lanthanide ions, divalent transition metal ions, trivalent transition metal ions and organic cations such as amphiphilic ammonium ions, quaternary ammonium cations and alkylpyridinium cations. Ion exchange can be carried out by means well known in the art. The process usually involves contacting the composition with a solution containing the desired cation at exchange conditions. Exchange conditions include a temperature of room temperature to about 100xc2x0 C. and a time of about 20 minutes to 4 days.
The crystalline compositions of this invention can be used in various hydrocarbon conversion processes. Hydrocarbon conversion processes are well known in the art and include cracking, hydrocracking, alkylation of both aromatics and isoparaffin, isomerization, polymerization, reforming, aromatization, hydrogenation, dehydrogenation, transalkylation, dealkylation, hydration, dehydration, hydrotreating, hydrodenitrogenation, hydrodesulfurization, methanation and syngas shift process. Specific reaction conditions and the types of feeds which can be used in these processes are set forth in U.S. Patent Nos. 4,310,440 and 4,440,871 which are incorporated by reference. Preferred hydrocarbon conversion processes are reforming aromatization, transalkylation, isomerization, dealkylation and dehydrogenation. Generally these processes are carried out at a pressure of about 10 to about 750 psig, a weight hourly space velocity of about 0.1 to about 30 hrxe2x88x921 with respect to the hydrocarbon, a gas hourly space velocity of about 10 to about 10,000 hrxe2x88x921 with respect to hydrogen and a temperature of about 100xc2x0 C. to about 650xc2x0 C.
The compositions of this invention can also be used to catalyze transalkylation. By xe2x80x9ctransalkylationxe2x80x9d is meant the process where an alkyl group on one aromatic nucleus is intermolecularly transferred to a second aromatic nucleus. A preferred transalkylation process is one where one or more alkyl groups of a polyalkylated aromatic compound is transferred to a nonalkylated aromatic compound, and is exemplified by reaction of diisopropylbenzene with benzene to give two molecules of cumene. The reaction conditions for transalkylation include temperatures in the range of about 100xc2x0 to about 250xc2x0 C., pressures in the range of 100 to about 750 psig, and a molar ratio of unalkylated aromatic to polyalkylated aromatic in the range from about 1 to about 10.
The following examples are set forth in order to more fully illustrate the invention. It is to be understood that the examples are only by way of illustration and are not intended as an undue limitation on the broad scope of the invention as set forth in the appended claims.